Embodiments of the present invention relate to an erosion resistant aerodynamic fairing and more particularly to an erosion resistant aerodynamic fairing for a rotor blade. Embodiments of the present invention are described herein by way of a practical example as an erosion resistant aerodynamic fairing for a wind turbine blade. However, it is readily applicable to other types of erosion-exposed surfaces, such as helicopter rotor blades, or fan blades.
Large three-bladed wind turbine blades typically rotate with tip speeds in the range of 75 to 100 meters per second. For some two-bladed turbines, the blades can rotate with a tip speed as high as 130 meters per second. This causes very severe erosion conditions at the tip of the blade as well as along the outer ⅓ of the leading edge, leading to blade damage in these areas. Although wind blades are typically expected to last for 20 years, this is often not the case due to the damage caused by erosion to the leading edge necessitating blade repair. However, repair of the leading edge is not easy since it is typically carried out with the blade still erected on the turbine. This also has significant cost and safety implications, particularly if the wind turbine is located offshore.
In order to reduce the damage caused by erosion, it is known to protect the leading edge of a wind turbine blade using a specialist paint coating. Such paints, for example “BladeRep LEP 9” available from Mankiewicz Gebr. & Co. of Hamburg Germany, have heavily filled and special formulations to give increased protection to the leading edge of a wind turbine blade. However, although erosion resistance is increased in the area to which the paint is applied, the protection provided by a specialist paint coating will diminish over time and will not last for the expected blade design life of 20 years without maintenance.
A further known example of an erosion protection measure for wind turbine blades is the use of metallic leading edges. However, these lead to an increase in the mass of the blade tip and, thus, increase the loads on the rest of the blade and the turbine. Metallic leading edges also increase the local stiffness of the blade, which can worsen aerodynamic performance, and can complicate the lightning protection systems required for the blade due to their conductive nature.
It is also known to apply a protective layer of thermoplastic film over the leading edge of a wind turbine blade. An example of this can be seen in FIG. 1, which shows the leading edge 118 of a fairing 110 for a wind turbine blade to which a protective layer of thermoplastic film 120 is fixed. Typically, the fairing 110 is formed from a composite laminate body 112 and the thermoplastic film 120 is post applied to the leading edge 118 as a thin (150 mm wide) tape with a layer of pressure sensitive adhesive 119. Such films offer good erosion resistance but are difficult to apply. Further, the quality of the bond between the thermoplastic film 120 and the laminate body 112 is dependent on the surface of the fairing 110 being free from grease and dust etc.
Alternatively, it is known to fix the thermoplastic film to the blade during the moulding of the fairing, as disclosed in International Publication No. WO2006/006593. In this method, layers of reinforcing fibre are placed on top of a film laid out against the mould surface, following which resin is applied to join the layers. Although this method provides an improved bond relative to post-applied films, it is difficult to control the quality of the interface between film and fairing and the quality of the substrate immediately beneath the film using this method.
A further known example of an erosion resistant fairing can be found in International Publication No. WO2010/117262. This fairing comprises a protective cover formed of a thermoplastic layer, a glass fibre mat and a cured epoxy resin layer by which the protective cover is attached to a composite body formed from fibre reinforced blade shells. The composite body and the protective cover are formed separately, and the protective cover is set in a recess in the composite body before the two components are fixed together using a layer of heat curable epoxy resin. However, this approach requires precise tolerance control of the parts to ensure that they fit together correctly and, as with the application of a thermoplastic film, the quality of the bond between the cover and the composite body is not easily controlled since it is dependent on the cleanliness of the attached surfaces.